Method and devices for avoiding knocking on failure of an anti-knock regulator

ABSTRACT

A device having a monitoring circuit for a knock control and a control circuit ( 10 ) which initiates substitute measures in the event of a fault in the knock control, depending on the output signal (f) of the monitoring circuit, is described. The control unit is designed, for example, so that the number of fuel injection operations per operating cycle of a cylinder of the engine is increased as the substitute measure.

BACKGROUND INFORMATION

[0001] The present invention relates to a method in which a firing angleand/or an ignition time of a gasoline or diesel engine having directinjection is regulated with the help of a knock control for preventingknocking during engine operation. In fault-free operation of a knockcontrol, fuel is injected once per operating cycle into the combustionchamber of a cylinder of the engine. In addition, combustion ismonitored by the knock control.

[0002] A known measure in the event of failure of knock control ofgasoline engines is a safety retardation of the firing angle relative tothe crankshaft position, the cylinder standing at 0° (crank angle) attop dead center, TDC. The firing angle is typically retarded by 12° to15° (crank angle). At such a firing angle, engine knocking does notoccur. However, one disadvantage of this is the loss of engineefficiency due to the safety retardation.

[0003] The problem on which the present invention is based is to providea simple method of preventing knocking in the event of failure of aknock control, so that it will also permit operation of the engine at ahigh efficiency even in the event of failure of the knock control. Inaddition, a device is also to be provided for this method.

ADVANTAGES OF THE INVENTION

[0004] The present invention creates a method having the method stepscharacterized in Patent claim 1. Refinements are characterized in thesubclaims.

[0005] The relationships in direct fuel injection are utilized for thepresent invention. Due to the design of the injection system, fuel isatomized in an especially fine spray. Different rotational movements ofair layers are achieved due to the air flow created in the intake andcompression strokes. There are different mixing ratios in the combustionchamber due to the injection of fuel in the intake stroke as well as thecompression stroke. Around the spark plug there is a rich fuel-airmixture surrounded by lean layers at the edge of the combustion chamber.Lean layers, i.e., layers in which the mixing ratio of fuel to air in kgis less than 1:14.8, are not as flammable as layers in which the fuelmixture is rich. A fundamental cause of knocking is spontaneous ignitionin boundary areas occurring in addition to the main ignition.

[0006] The present invention is based on the finding that whereas theknocking tendency of direct injection engines is already reduced, it maybe further decreased by multiple injection and/or a different injectionquantity during a operating cycle of the engine. For example, in thecase of a gasoline engine, there is a single injection during the intakestroke and the compression stroke or the injection quantity isincreased. This measure yields a very large gradient of the mixing ratiofrom the spark plug area to the edge of the combustion chamber. Thisgradient counteracts engine knocking. Since knocking is already limitedin this way, it is no longer necessary to make a safety retardation orat any rate a smaller angle may be used for the safety retardation. Aconsiderable loss of engine efficiency may be prevented by the methodaccording to the present invention, because the firing angle need not beretarded by the usual large crank angle values of 12° to 15°.

[0007] In a refinement of the method according to the present invention,the firing angle is controlled as a function of the engine rotationalspeed and/or engine load after the change in injection quantity. Theengine rotational speed and engine load are the essential characteristicvariables which influence the firing angle. However other characteristicvariables may also be taken into account to improve the control.

[0008] The present invention also relates to a device for preventingknocking in the event of failure of a knock control. This device makesit possible to implement the method steps of the method according to thepresent invention and it includes a monitoring circuit for a knockcontrol and a control unit which initiate sustitute measures to preventknocking in the event of a fault in the knock control, depending on theoutput signal of the monitoring circuit. The control unit is designed sothat the substitute measure in the case of a gasoline engine involves,for example, a transition from a single injection of fuel per operatingcycle of a cylinder of the engine to two injections of fuel peroperating cycle. The technical effects and considerations describedabove for the method according to the present invention also apply tothe device according to the present invention.

[0009] In a next refinement, the control unit controls the firing angleas a function of the engine rotational speed and/or engine load. Thusthe essential characteristic variables which are crucial for theadjustment of the firing angle are also taken into account withappropriate measure. Although regulation in a closed-loop controlcircuit is no longer possible, control is performed nevertheless to beable to adjust an acceptable firing angle.

DRAWINGS

[0010] Exemplary embodiments of the present invention are explainedbelow on the basis of the accompanying drawing, which shows:

[0011]FIG. 1 a block diagram of part of a control circuit for activatingmultiple injection in the event of failure of a knock control, and

[0012]FIG. 2 a block diagram of another part of the control circuit.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0013]FIG. 1 shows a block diagram of part of a control circuit 10 foractivating multiple injection in the event of failure of a knock controlof a direct injection gasoline engine (not shown). Control circuit 10contains an AND logic element 12 at whose one input an activation signalkr is applied and at whose other input a fault signal f is applied.Activation signal kr and fault signal f are generated by a controller ofthe firing system. Activation signal kr has the switch state logic ONEwhen the knock control is to be active. Fault signal f has the switchstate logic ONE when there is a disturbance in the knock control. ANDlogic element 12 gates the values of the activation signal and the faultsignal according to the logic AND function and outputs a request signalhkss whose signal value of logic ONE causes switching over from singleinjection to double injection. The letter sequence hkss denoteshomogeneous anti-knock safety setpoint.

[0014] The method steps and components required for switching over thetype of injection are not the object of the present invention andtherefore will not be explained in greater detail. For example, theposition of the throttle valve may be altered in switching over. Inaddition, the injection nozzles are actuated according to anotherscheme.

[0015] If the switching over is performed successfully, the signal valueof a control signal hks (homogeneous anti-knock safety protection) isswitched to logic ONE. However, if the switching over cannot beperformed, the signal value of control signal hks remains at the valueof logic ZERO. For example, this is the case when the fault causing thefailure of the knock control also prevents the system from switchingover to double injection.

[0016]FIG. 2 shows the other part of control circuit 10. Control circuit10 contains another AND logic element 20 at whose one input is appliedfault signal f and control signal hks at its other input. AND logicelement 20 gates the signal values applied to its inputs according tothe logic AND function. The output of AND logic element 20 is connectedto the input of a NOT element 22 which outputs at its output a signalvalue inverted relative to the signal value applied at its input. Theoutput of NOT element 22 is connected to the switching over input of aswitching unit 24. Depending on the signal at the switching input,switching unit 24 switches between two switch states 0 and 1.

[0017] Control circuit 10 also contains an engine characteristics mapunit 26 in which are stored various ignition characteristics maps forthe double injection mode of operation. Engine characteristics map unit26 has a plurality of inputs, of which FIG. 2 shows inputs for inputtingan rotational speed signal nmot and a load signal rl (relative airfilling). Engine characteristics map unit 26 reads a value for thefiring angle out of a memory unit (not shown), depending on the signalvalues of the rotational speed signal nmot and load signal rl, andoutputs an engine characteristics map value kfw. Engine characteristicsmap unit 26 may be either an analog or digital unit. Then rotationalspeed signal nmot, load signal rl, and engine characteristics map valuekfw are either analog or digital signals accordingly.

[0018] Engine characteristics map value kfw is applied to the one inputof switching unit 24 and is output at the output of switching unit 24 inswitch state 0 of switching unit 24 (see output signal 28). The otherinput of switching unit 24 is connected to output signal sv of a knockcontrol unit (not shown) for retardation, adjusting the firing angle ina regulating operation. Output signal sv goes to the output of switchingunit 24 in switch state 1 of switching unit 24.

[0019] Control circuit 10 contains another switching unit 30 at whoseswitching input activation signal kr is applied. Depending on the signalvalue of activation signal kr, switching unit 30 operates in two switchstates 0 and 1. Signal value of logic ZERO is constantly applied at theone input of switching unit 30. If control signal kr has the value logicZERO, then in switch state 0 of switching unit 30, value ZERO applied atthe input is output at the output of the switching unit and is used asinput signal dwkrz for a firing angle setpoint unit 32.

[0020] The other input of switching unit 30 is connected to the outputof switching unit 24, so that in switch state 1 of switching unit 30,output signal 28 stipulates the course of input signal dwkrkz.

[0021] Firing angle setpoint unit 32 also has an input for a cylindercounting signal zzyl whose signal value indicates the cylinder in whosecombustion chamber an ignition is to be executed. Firing angle setpointunit 32 outputs a firing angle signal 34 which specifies the firingangle for all cylinders of the engine in succession.

[0022] The part of control circuit 10 shown in FIG. 2 operates asfollows with fully functional knock control. Fault signal f and controlsignal hks have the signal value of logic ZERO. A logic signal 36 at theoutput of AND logic element 20 therefore also has the signal value oflogic ZERO. A switching signal 38 at the output of NOT element 22 hasthe signal value of logic ONE because of the inversion of logic signal36, so that switching unit 24 is switched to switch state 1. Outputsignal sv output by anti-knock regulating unit stipulates the course ofoutput signal 28. If activation signal kr has a value of logic ZERO, noknocking is detected and no knock control is necessary. In this caseswitching unit 30 has switch state 0 so that input signal dwkrz has thevalue of logic ZERO. Firing angle setpoint unit 32 outputs a firingangle signal 34, which is not corrected with regard to knock control.

[0023] However, if activation signal kr has the value of logic ONE inthe case of fully functional knock control because knocking is detected,then switching unit 30 operates in switch state 1. In switch state 1,output signal 28 of switching unit 24 stipulates the course of inputsignal dwkrz. Firing angle setpoint unit 32 therefore outputs a firingangle signal 34 which is corrected with the help of the firing anglespecified by the knock control to counteract engine knocking.

[0024] If there is a disturbance in the function of the knock control,then fault signal f first has a value of logic ONE and control signalhks has a value of logic ZERO. Logic signal 36 therefore continues tohave a value of logic ZERO. The operation of control unit 10 correspondsto the operation described above. However, if the signal value ofcontrol signal hks is switched to the value ONE on the basis of theprocesses illustrated above in FIG. 1, then the value of logic signal 36changes to the value of logic ONE. Control signal hks has the value oflogic ONE as soon as the system switches to double injection. The signalchange in logic signal 36 results in a change in the signal value ofswitching signal 38. Switching signal 38 then has the value of logicZERO so that switching unit 24 is switched to switch state 0. Enginecharacteristics map value kfw which depends on the current enginerotational speed (see rotational speed signal nmot) and on the currentengine load (see load signal rl) then stipulates the value of outputsignal 28. If no knocking of the engine is detected, activation signalkr has the value of logic ZERO and the firing angle setpoint unit doesnot perform a correction of the firing angle with regard to knockcontrol. However, if knocking of the engine is detected, the activationsignal kr has the value of logic ONE. Switching unit 30 operates inswitch state 1 and the course of output signal 28 stipulates the courseof input signal dwkrz. Firing angle setpoint unit 32 corrects the firingangle so that knocking is counteracted. The engine characteristics mapstored in engine characteristics map unit 26 for the double injection isused for correction.

[0025] If engine knocking no longer occurs, then activation signal kragain has the value of logic ZERO and switching unit 30 switches back toswitch state 0. Fault signal f and control signal hks remain at thevalue of logic ONE, however.

LIST OF REFERNCE NOTATION

[0026]0,1 switch state

[0027]10 control circuit

[0028]12 and logic element

[0029] kr activation signal

[0030] f fault signal

[0031] hkss request signal

[0032] hks control signal

[0033]20 AND logic element

[0034]22 NOT element

[0035]24 switching unit

[0036]26 engine characteristics map unit

[0037] nmot rotational speed signal

[0038] rl load signal

[0039] kfw engine characteristics map value

[0040]28 output signal

[0041] sv output signal

[0042]30 switching unit

[0043] dwkrz input signal

[0044]32 firing angle setpoint unit

[0045] zzyl cylinder counting signal

[0046]34 firing angle signal

[0047]36 logic signal

[0048]38 switching signal

What is claimed is:
 1. A method of preventing knocking in the event offailure of a knock control, in which a firing angle and/or ignition timeof an engine having direct injection is regulated by using a knockcontrol to prevent knocking during engine operation, in fault-freeoperation of the knock control, fuel is injected into the combustionchamber of a cylinder of the engine at least once per operating cycle,and the combustion is monitored by the knock control, wherein in theevent of a disturbance in the knock control, the quantity of fuelinjected and/or the number of injection operations per operating cycleis altered.
 2. The method as recited in claim 1, wherein in the event ofa disturbance in the knock control of a gasoline engine, fuel isinjected at least once more per operating cycle of the cylinder than infault-free operation of the knock control.
 3. The method as recited inclaim 1 or 2, wherein in the event of a disturbance in the knockcontrol, the firing angle and/or the ignition time is controlled as afunction of the operating point of the engine, e.g., the rotationalspeed and/or load.
 4. A device for preventing knocking in the event offailure of a knock control, having a monitoring circuit for a knockcontrol, which regulates a firing angle and/or ignition time of anengine having direct injection, and having a control unit (10) whichinitiates substitute measures to prevent knocking in the event of afault in the knock control, depending on the output signal (f) of themonitoring circuit, wherein the control unit (10) is designed so that asa substitute measure, the injection quantity and/or the number ofinjection operations of fuel per operating cycle of a cylinder of theengine is altered.
 5. The device as recited in claim 4, wherein thenumber of injection operations per operating cycle is increased as asubstitute measure in a gasoline engine.
 6. The device as recited inclaim 4 or 5, wherein the control unit (10, 26) controls the firingangle and/or the ignition time as a function of the operating point ofthe engine, e.g., the rotational speed and/or load.
 7. The device asrecited in claim 6, wherein the control unit (10) contains a firstswitching unit (24) which switches over as a function of the outputsignal (f) of the monitoring circuit, the control unit (10) contains asecond switching unit (30) which is connected at the input side to theoutput of the first switching unit (24) and switches over as a functionof a signal (kr) which signals the knock control.
 8. The device asrecited in claim 7, wherein for generating the switching signal (38) forthe first switching unit (24), the control unit (10) contains a logicelement (20) at whose inputs the output signal (f) of the monitoringcircuit and a control signal (hks) are applied, signaling the transitionto the substitute measure, and the output of the logic element (20) isconnected to a switching input of the first switching unit (24),preferably with the insertion of a NOT element (22).
 9. The device asrecited in one of claims 4 through 8, wherein the control unit (10)contains an additional logic unit (12) at whose inputs the output signal(f) of the monitoring circuit and a signal (kr) which signals the knockcontrol are applied, and the output of the additional logic unit (12) isconnected to a unit for controlling the injection operations.